test: I2C/PCA9548 unittest

artiq/coredevice/i2c.py

@@ -46,6 +46,19 @@ class PCA9548:
         finally:
             i2c_stop(self.busno)
 
+    @kernel
+    def readback(self):
+        i2c_init(self.busno)
+        i2c_start(self.busno)
+        r = 0
+        try:
+            if not i2c_write(self.busno, self.address | 1):
+                raise I2CError("PCA9548 failed to ack address")
+            r = i2c_read(self.busno, False)
+        finally:
+            i2c_stop(self.busno)
+        return r
+
 
 class TCA6424A:
     def __init__(self, dmgr, busno=0, address=0x44):

artiq/test/coredevice/test_i2c.py

@@ -0,0 +1,25 @@
+import os, unittest
+
+from artiq.experiment import *
+from artiq.test.hardware_testbench import ExperimentCase
+
+
+class I2CSwitch(EnvExperiment):
+    def build(self):
+        self.setattr_device("core")
+        self.setattr_device("i2c_switch")
+
+    @kernel
+    def run(self):
+        passed = True
+        for i in range(8):
+            self.i2c_switch.set(i)
+            if self.i2c_switch.readback() != 1 << i:
+                passed = False
+        self.set_dataset("passed", passed)
+
+
+class I2CTest(ExperimentCase):
+    def test_i2c_switch(self):
+        self.execute(I2CSwitch)
+        self.assertTrue(self.dataset_mgr.get("passed"))